The present invention relates to a sputtering target for producing a metallic glass membrane that generates few nodules or particles, and to its manufacturing method.
An amorphous metallic glass thin membrane can be used as a hydrogen separation membrane or a magnetic film. Nevertheless, metallic glass is a multi-component system of a ternary compound system or greater, and there are problems with the conventional manufacturing method of a target in that segregation will occur during melting or casting, or crystallites will grow during solidification.
Such segregation and grown crystallites will cause the generation of nodules and particles, and there is a problem in that the sputtered membrane would be defective. Further, adverse effects are also inflicted on the sputtering characteristics.
In recent years, there is increasing demand for efficiently separating hydrogen in fuel cells and other items. Generally speaking, since hydrogen produced from fossil fuel or water contains various impurities due to its manufacturing method, it is necessary to perform purification upon separating such impurities in order to obtain high purity hydrogen.
As the purification method, the PSA (Pressure Swing Adsorption) method, membrane separation process, cryogenic distillation method, absorption method and the like may be used. Among the above, the membrane separation process employing a metallic membrane is the only process that is able to manufacture ultrahigh purity hydrogen, which can be put into practical application, at a high yield and with sufficient speed.
As the hydrogen separation membrane, numerous materials that do and do not contain Pd (since Pd is costly) have been proposed in the past. For instance, refer to “Developmental Status of PEFC Electrode, Separator and Hydrogen Separation Membrane Employing Metallic Glass” written by Naotsugu Meguro published in Fuel Cells, Vol. 2, No. 2, 2003, pages 13 to 17. In particular, there is indication that a Ni—Nb—Zr metallic glass alloy is effective. For instance, refer to “Hydrogen Permeation Characteristics of Ni—Nb—Zr Metallic Glass Alloy” written by Shinichi Yamaura et al. published in (680) The Japan Institute of Metals, Spring Convention Lecture Summary (2003), page 346 and the publication of Shinichi Yamaura et al. titled “Hydrogen Permeation Characteristics of Melt-Spun Ni—Nb—Zr Amorphous Alloy Membranes” in Materials Transactions, Vol. 44, No. 9 (2003) pp. 1885-1890. Although the ultrafine processing technique, in particular the deposition technique, is primarily used for forming a hydrogen gas separation membrane, since even the crystal grain boundary of the formed film will become a problem in ultrafine processing, demanded is a deposition method capable of forming a film without a crystal grain boundary; that is, an amorphous membrane or an equivalent film, upon forming a thin membrane.
Meanwhile, as methods of manufacturing bulk metallic glass, proposed are a water quenching method of obtaining virgulate metallic glass by quenching the molten metal enclosed in a silica tube, a method of performing arc melting and quenching with a water-cooled copper mould, a clamping casting method of obtaining metallic glass by melting metal on a copper mold and thereafter pressing this with a cope and quenching the product, a method of performing injection molding at high pressure and quenching this in a copper mold, and a method of manufacturing a metallic glass wire rod by solidifying molten metal on a rotating disk. For instance, refer to “Manufacturing Method of Bulk Metallic Glass” published in Functional Material, June 2002 Edition, Vol. 22, No. 6, pages 26 to 31.
Nevertheless, since each of these manufacturing methods is a manufacturing method from molten metal and is subject to quenching, it is necessary to devise the apparatus to meet the quenching conditions, and there is a drawback in that the cost would be extremely high. Further, even when forming a thin membrane, there are limitations, and there is a problem in that it was only possible to form a thin membrane of up to 30 μm in the past.